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I'm looking at a Resmed S8 as a camping Cpap to runoff a deep cycle battery. I found a little used S9 but Resmed does not support the unit any more and I haven't been able to find a Resmed DC power connection kit anywhere online. Does any one here have any suggestions?

At least they list them on their web sites. Have you called and found they aren't available?

I know S9 machines are booby trapped to not work without the ResMed adapters even if you get the right voltages. I'm not sure S8 machines will run off of 12V directly or not. ResMed has dire warnings that you need the ridiculously overpriced ResMed DC-DC converter for the S8 machines.

I do recall hearing that S8 and Respironics machines use the same DC plug but opposite polarities.

If you use a DC-AC inverter, don't use the it with the S8 machine, or it may damage the humidifier. S9 machines work OK with inverters.

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(02-01-2015, 06:39 PM)Breathetonight Wrote: I'm looking at a Resmed S8 as a camping Cpap to runoff a deep cycle battery. I found a little used S9 but Resmed does not support the unit any more and I haven't been able to find a Resmed DC power connection kit anywhere online.

Do you mean you found a little-used S8?

I think it is important to use the proper DC-DC converter to replace the machine's normal 115VAC Power Adapter, because using an inverter to produce 115VAC (to use the normal AC Power Adapter) would be much less efficient, requiring perhaps 40% or 50% greater reserve capacity in the deep discharge battery, which would cost more to get a bigger and heavier battery or would cost in terms of allowing less run time before the battery would become discharged.

Prices for used S9 machines are becoming more affordable these days. (For example, from Supplier #2 on the Supplier List.)

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I know the S9 is a 24 volt blower. I was under the impression that the S8 was a 12V system? Just wired backwards?

VERIFY EVERYTHING I SAY HERE BEFORE ACTING ON IT OR PROCEED AT YOUR OWN PERIL. It has been a long time since I messed with any S8 equipment and i have not had the opportunity to sleep at a Holiday Inn Express since then... In any case, the sneaky boogers at Resmend wired the DC plug backwards so nobody else's plug would work. IIRC it is center pin negative, outer jacket positive. So if you make your own plug, verify that .... And verify it before using somebody else's dc cord. Also IIRC the S8 used a 25 mm plug, but I could be wrong on that. As I said, it's been a couple years since my S8 died and went under that great slow recycling mountain on the southern edge of town.

The old s8 cpap apap needs a pure sine wave inverter. Using a normal modified sine wave inverters will over time burn out the blower motor and compliance electronics.

I ran an s8 on a pure sine wave inverer in the truck for years with no problems.

The s9. has a direct 12v power supply. That saves on battery drain.

Running anything off 12 battery via inverter will result in significant power loss through the inverter. This power loss gets really bad if you're using the inverter near it's wattage limits..

Most cpap at max pressure and max humidification draw. 185 watt 110v AC power . Plan on using a 400 watt inverter directly wired to battery. Use good heavy gauge cable from the inverter to battery. Light cable will mess up battery drain by overheating.

(02-04-2015, 04:26 AM)truckerdad57 Wrote: The old s8 cpap apap needs a pure sine wave inverter. Using a normal modified sine wave inverters will over time burn out the blower motor and compliance electronics.

Not according to ResMed. All the S8 machines are specified to run on MSW inverters as long as you remove the humidifier.

(02-04-2015, 04:26 AM)truckerdad57 Wrote: Most cpap at max pressure and max humidification draw. 185 watt 110v AC power . Plan on using a 400 watt inverter directly wired to battery. Use good heavy gauge cable from the inverter to battery. Light cable will mess up battery drain by overheating.

Your number is too high. My S9 with pressure of 16 and humidification at 5 draws about 30 watts average on the AC power line. Measured with a Kill-a-watt device.

Check the ResMed PDF document for numbers for many operating conditions.

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